Title:

Branes and black holes in string theory

The goal of this thesis is to address several issues in gravitational physics, in particular black hole physics, within a quantum mechanical framework. Of course this requires the existence of such a quantum mechanical theory of gravity. Superstring theory is a consistent perturbative theory of gravity. However, many aspects of the theory turn out to be nonperturbative and in this sense the theory is still under construction. The theory of strings contains a large variety of pdimensional spatially extended objects, now called pbranes. These pbranes are dynamical objects embedded in spacetime: they interact between each other, intersect each other and bound themselves together. In this thesis I shall study some of these pbrane configurations. I shall start by using supergravity which is a large distance (low energy) approximation to string theory, to construct many new pbrane configurations. The emphasis will be on the technics to construct the supergravity solutions describing these configurations and on the symmetries of the underlying theory that render their existence. I shall not attempt to give a complete classification of the pbrane configurations folklore nor shall I address issues related to the global structure of the corresponding gravitational geometry. In turn, the focus will be on the microscopic and quantum mechanical description of some of these pbrane configurations, namely the Dbrane bound states. In particular, I shall study in detail a D5 brane configuration with a constant magnetic field on its worldvolume. The gravitational counterpart is a fivedimensional black hole. The quantum mechanical description of this system will allow the calculation of the BekensteinHawking entropy from counting microscopic states of the Dbrane system. The scattering of a scalar particle off the black hole (and therefore Hawking radiation) are also studied. I end by making a proposal for an effective string description of black hole dynamics. In the process I shall use results in perturbative string theory, gauge theory and gravitational theory. In this sense, this thesis is rather interdisciplinary which is a remarkable characteristic acquired by superstring theory.
